Supervisory circuit



F. P. GIRONE ETAL 3,114,007 suPERvIsoRY CIRCUIT Dec. 10, 1963 E C/RONE J. A. HARR 7'. /V. LOW/QV E G. R/D/NGER %0Y ATTORNEY /N VENT ORS Dec- 10 1953 F. P. GIRONE ETAL 3,114,007

sUPERvIsoRY CIRCUIT 3 Sheets-Sheet 2 Filed July l, 1959 HMQ 5,5% kwh.

/A/l/ENTO/PS 7. N By l? G mu X DeC- 10, 1963 F. P. clRoNE ETAL 3,114,007

SUPERVISORY CIRCUIT 5 sheets-sneed s Filed July l, 1959 5 i 212% /NVE/VTORS I' LOW/H,

By Zi? G RIDING/ER ATTORNEY United States Patent O Iii-aol; l?. Cirone, Dover, .lohn A. Herr, Morris Plains, and 'llerreil N. lisos-'ary and Philip G. Ridinger, Ecoutez-a, NJ., assigncrs to Beil Telephone Laboratories, incorporated, New Yer-lr, NX., a corporation or New York Filed .l'uiy l, 1959, Ser. No. 824,294 3l Claims. ('Sl. 179-48) This invention relates to telecommunication systems and more particularly to supervisory systems to be ernployed in telecommunication systems for transmitting intelligence of a supervisory nature from a remote location to a central control location.

ln various types of telecommunication systems, it is necessary that an indirect control of a plurality of units, such as subscriber telephone lines be effected by a central control location remote from these units and not in direct electrical connection therewith. The plurality of units are terminated in and directly controlled by a remote station which is, in turn, directly controlled by the central control location. Generally supervision information with respect to these remote units has been transmitted to the central control location in the form of information identifying the immediate state conditions of these units. ln accordance with our invention, as set forth in detail subsequently, the intelligence transmitted is indicative of the particular change conditions of these units, as distinguished from immediate state conditions, and the central location receives such intelligence as change information relating to a particular unit.

The central location takes necessary action in cognizance of such determined change condition to regulate the operation of the remote unit by the transmission of control intelligence indicating such operation to the remote station, Such control intelligence is developed at the central ollice location upon an awareness of the particular change in the operation of a particular one of the units and the action required to be taken by the remote station thereon.

The present invention nds practical application in automatic telephone systems or" the type where either a single or multiple concentration of a plurality of served substations is had through a smaller number of trunks emanating from the central oilice location. While the description of this invention will be given in conjunction with line concentrator telephone systems, it will become evident that the concepts herein contained may lind application in any system wherein a supervision of the change condition of each of a plurality of units is desired at a central location to which such units are normally unconnected.

ln line concentrator telephone systems, a portion of the switching equipment is located remotely from the central oflcelocation and operates as a slave unit with respect thereto to affect a connection between one of a plurality of substations served thereby and an idle line emanating from the central office location. The supervisory systems priorly employed in such telephone systems are situated partly at the remote location and partly at the central otlice location. The intelligence provided by such prior systems to the central oice location, however, is in the form of state condition information, Le., on-hook or ofi-hook, and further processing thereof is necessary to convert such information to change condition information, i.e., service request, answer, hang-up, and flashing. A conversion from state condition information to change condition information at the central office location is requisite to the determination thereat of necessary actions to be performed by the switching equipment and the generation and transmission of appropriate control intelligence thereto for initiating such actions. A

ice

conversion from state condition to change condition is elected at the central ollice location by continuously sampling the immediate state condition of the substation which is compared with the state condition thereof as determined by a previous sampling stored in appropriate memory units thereat.

The main impetus given to the employment of line concentrator telephone systems has been the attempt to reduce the unit cost per substation. ln present day telephone systems, a large portion of the unit cost per substation is directly attributable to the cost of installation and operation of the individual links used to interconnect the individual substations to the central oce location. This unit cost per substation has been substantially reduced in line concentrator telephone systems through the sharing by a plurality of substations of a fewer number of links to which each may be selectively connected to the central ohce location. However, a portion of such unit cost per substation can still be laid to the cost of complex supervisory systems employed in line concentrator telephone systems for the determination of the change conditions of the served substations. For example, present day line concentrator telephone systems utilize control pairs of wires for the continuous transmission on a time division basis of the state condition of the served substations from the scanning means of the line concentrator unit to the central otlice location; necessitate complex units at the central oilice location to effect a reception, comparison and conversion of the received state condition information to change condition information; require a direct-current connection between the central office location and a substation upon a communication connection having been established for the continuous supervision of the state condition of a substation at the central olhce location; utilize additional scanning means at the central oilice location for a sampling of such communication connection to determine the immediate state condition of the particular substation; and require the addition of means to insure the proper maintenance and operation of the switching equipment of the line concentrator unit.

A general object of this invention is the direct determination of the change condition of a plurality of substations served in a line concentrator telephone system.

More specifically, it is an object of this invention to provide supervisory means wherein the change condition, as distinguished from the immediate state condition, of each or" a plurality of substations served in a line concentrator telephone system may be directly transmitted to the central office location.

Another object of this invention is to provide supervisory means for line concentrator telephone systems or the type wherein alternating-current coupled networks are employed as communication paths.

Still another object of this invention is to provide a supervisory means for line concentrator telephone systems wherein the operation of the switching network of the line concentrator unit may be simultaneously monitored in addition to the change condition of each substation being directly determined.

A further object of this invention is to provide for the supervision of a plurality of substations served by a line concentrator elephone system, such supervision being eilected through a transmission of a minimum of intelligence between the line concentrator unit and the central otlice location in such system.

A still further object of this invention is to provide a supervisory means for line concentrator telephone systems wherein the eliect of spurious pulses is eliminated.

The specific objects of this invention are achieved by the provision of means for continually generating a first and second series of superaudible frequency pulses to and terminating calls.

be each directed oppositely between the loop terminals and the link terminals, respectively, of the switching network of a line concentrator unit and for monitoring on a time basis the appearance of such pulses at each of these terminals to develop supervisory information. The appearance of the first and second series of pulses, which have no logical significance in themselves, through the switching network is conditioned upon the closure of a particular one of the crosspoint connections therein and upon the immediate state condition of the substation -to which a communication connection has been provided therethrough. The source of the-rst series of pulses is connectable to the loop terminals of the switching network through a plurality of transmission gates associated one with each substation or with each group of substations provided with party line service. Each transmission gate is responsive to currents in the associated substation loop to inhibit or allow the appearance of the iirst series of pulses at the loop terminals of the switching network during an off-hook and an on-hook state condition, respectively, thereof. Ihe source of the second series of pulses is directly connected to the link terminals of the switching network. A feature of this invention relates to the provision of means for generating the first and second series of pulses to appear on both the loop terminals and the link terminals, respectively, of vthe switching network of a line concentrator unit to serve as monitoring signals.

Another feature of this invention relates to the provision of scanning means for the loop terminals of the switching network, which means is operative to direct an intelligence pulse to the central oilice location in response to the absence of both the first and second series of pulses thereat.V The loop scanning means operates to directly indicate a service request change condition of a substation to the central office location upon the absence of the first series of pulses at the loop terminals of the switching network resulting from the inhibitive action of the transmission gate associated therewith. the second series of pulses is also absent from the loop terminal of the'switching network as the crosspoint connection to be provided for the communication connection remains open for a short interval of time prior to the closure thereof by the central oiiice location. Upon the closure of the crosspoint connection, the second series of pulses appears at the loop terminals of the switching network to'inhibit the loop scanning means for the duration of closure thereof. Accordingly, the detection of the second series of pulses by the loop scanner means is indicative of the continuity of crosspoint closure and provides for the monitoring thereof. A false opening of the crosspoint connection during a communication interval for any reason causes the loop scanning means to direct an intelligence signal to the central office which is distinguishable thereat as a crosspoint failure indication. The signals developed by the loop scanning means to indicate a service request condition and a crosspoint failure are identical. However, this ambiguity is resolved by another feature of this invention which relates to the provision of appropriate memory circuits at the central office location adapted to recognize the proper sequence of substation change conditions for originating Accordingly, a second reception of an intelligence signal from the loop scanning means subsequent to a direction by the central oliice location for the establishment of a communication connection and, similarly, upon the closure of a crosspoint connection and prior to the proper release thereof is resolved to indicate a crosspoint failure.

Still another feature of this invention relates to the provision of scanning means for the link terminals, which means is responsive only to the iirst series of pulses appearing on the loop terminals of the switching network. The crosspoint connection associated with a communication connection to a particularV substation is necessarily closed prior to a hang-up change or an answer change At this time,

condition in the operation of that substation. Further, the immediate state conditions of the substation are necessarily opposite prior to the hang-up change and answer change conditions, i.e., the substation is necessari-ly onhook prior to an answer change condition and off-hook prior to a hang-up change condition. Thus, due to the peculiar operation of the transmission gate assocated with each substation, a hang-up change condition of particular substation, i.e., a change from off-hook state condition to `on-hook state condition subsequent to the establishment of a communication connection thereto, is indicated by the appearance following an absence of the first series of pulses at the link terminals of the switching network. Similarly, but conversely, an answer change condition, i.e., a change from an yon-hook state condition to of-hook state condition subsequent to the establishment of a communication connection thereto, is indicated by the absence following the appearance of the tirst series of pulses at the link terminals of the switching network. Accordingly, answer and hang-up change conditions are characterized by a previous closure of the crosspoint connection, which in effect operates as a memory element, and the absence or appearance, respectively, following an opposite state of the first series of pulses on the link terminals of the switching network. The link scanning means is operative to direct the first series of pulses appearing at the link terminals of the switching network to coincidence gating and detector nieans associated therewith.

A further feature of this invention relates to the provision of coincidence gating and detector means associated with and responsive 4to each ofthe loop scanning and link scanning means. To reduce the susceptibility of the supervisory system to spurious pulses, the outputs of each of the loop scanning means and link scanning means are applied to associated gating means to which are coincidently applied those pulses of the first and second series to which each is intended to be responsive. Accordingly, the first and second series of pulses are employed as local reference signals in addition to being employed as monitoring signals by the supervisory system. The detector means are responsive to the coincidence gating means to develop a characteristic indication of the appearance of the iirst and second series of Vpulses through the loop scanning and link scanning means.

A still further feature of this invention relates to the provision of memory and logic circuitry means at the remote location for the direct determination of a change condition in the operation of a particular substation and the generation of characteristic indications thereof. As the absence of the iirst series of pulses at a particular loop terminal and a corresponding link terminal connected thereto through the switching network is indicative of the substation state condition, the logic circuitry means are provided with inverter means to provide a positive characteristic indication of the Vabsence of a direct-current potential at the output of each of the detectors associated with the loop scanning means and link scanning means. With respect to the generation of characteristic indications of a hang-up change and answer change conditions of a substation, scanning selector means are provided to nondestructively read out on a time basis the memory means in which are recorded the prior state conditions, i.e., first series of pulses present or absent, of each link during the progress of a call. The output of the scanning selector means Vis directed to the logic circuitry means which are operative to compare such reading with the output of the detector means associated with the link scanning means. The logic circuitry means are adapted to develop appropriate change condition indications if there is disagreement between the prior state condition of each link as recorded in the memory means and the immediate state condition of the link as indicated by the output of the detector means associated with the link scanning means. The memory circuit is adapted, if such a disagreement is assessed, to store the immediate state condition of the individual link as a reference for future comparisons. stored in the memory means upon the initial appearance t the first series oi pulses at the link terminals oi the switching network and through the link scanner means and, conversely, a non-readable condition upon the initial absence thereof. For the generation of hang-up change and answer change conditions, inverter means are provided for a characteristic indication oi the absence of the direct-current potential at the output of the detector associated with the link scanner means and, similarly, of a non-readable condition with respect to a link circuit as stored in the memory unit and sensed by the scanning selector means. As is more fully described below, the sequences or readable and non-readable conditions stored in the memory means for ori nating and terminating calls are not identical.

{oweven still another feature of this invention relates to the provision of means for controlling the memory means to record the proper sequences of readable and non-readable conditions pertaining to a particular link employed for a communication connection and adapted so as to rfa-normalize the memory means upon a crosspoint release which signilies the termination of both originating and terminating calls. Accordingly, through the use of such inverter means, a comparison ot' successive state conditions of each link with the information stored in the memory means with respect thereto during the progress of a call indicates directly the hang-up change and answer change conditions of a particular substation through appropriate AND gate means.

An additional feature of this invention relates to the provision or" means for delaying the operation of each of the link scanner, loop scanner and scanning selector means with respect to the counter unit by which they are driven. IThe advance pulses directed from the central oilice to step the counter unit also serve to enable the transmission of the change condition or" the substation to the central office through the appropriate AND gate means. ln order to compensate for the delay introduced by the operation of the individual detector circuits in normalizing `to the a sence or presence of the rst and second series of pulses, the link scanner, loop scanner and scanning selector means are normally advanced a single position with respect to the counter unit by which they are driven. The appearance of an advance pulse from the central oilicc to the counter unit is momentarily delayed until the output oi the detector circuits are sampled by the enablirv of the appropriate ANI) gate means thereby and w lich thereupon becomes effective to step the counter unit to allow the detector circuits to normalize with respect to the next position prior to the appearance of a subsequent advance pulse.

An additional feature of this invention relates to the manner by which the link scanner and the scanning seector means are operated in relation to the operation of the loop scanner means. rThe loop scanner means is operative on a one-out-of-Y basis where Y is equal to the number of substations served, but the loop scanner controlling rneans is eilective to control the link scanner and the scanning selector means on a one-out-of-X basis where X is equal to the number of link circuits available. Accordingly, the link scanner and scanning selector means are cyclically operated Y/X or Z times for each cyclic operation for the loop scanner means.

A distinguishing feature ot this invention relates to thc operation of the supervisory system to provide monitoring information of the proper operation of the crosspoint connections comprising lthe switching network. Each oi the change condition indications relating to the operation of a substation has a dual or ambiguous significance due to the tact that the system conditions under which each is developed are not peculiar thereto. This lack of peculiarity results from the fact that a finite inter- More specifically, a readable condition is` val of time necessarily elapses between the actual change in the operation condition of a particular substation and the affecting oi an appropriate crosspoint in the switching network by the central oilice location. lowever, the proper significance to be attached to the supervisory information is resolved at the central office location by a comparison of the occurrence of the information pulse with respect to the state condition or the communication connection, ie. such connection has either been effected or is to be etrected or disconnected, as recorded on a link basis in appropriate memory means thereat. For example, the detection of a crosspoint failure indication was mentioned above with respect to the operation of the loop scanning means and the generation of a service request change condition indication. With respect to the two change conditions possible in the controlled operation of the crosspoint connections, i.e., crosspoint closure and crosspcint release, the system conditions which result therefrom are such as to cause the generation oi indications which, though identical to hang-up condition indications for terminating calls or to the absence of repeated service request change condition indications and to answer change condition indications for both terminating and originating calls, respectively, are resolved by appropriate memory means at :the central oilice location upon the occurrence thereof during that interval in which a communication connection is to be effected or disconnected, respectively. Each of these indications appears at the central office location subsequent to a control action thereby to alert the common control to the presence of supervisory information initiate a processing thereoi by the common control unit located thereat which includes the appropriate memory means.

1Ehe methods of monitoring the grocer closure of crosspoint connections in the case of terminating calls and originating calls are dissimilar. ln the case for originating calls, for example, the substation is necessarily in an oil-hook condition and the transmission gate associated therewith inhibits the appearance of the first series of pulses at the loop scanning means. Accordingly, the loop scanning means are operative to continually develop double-meaning service-request indications until the centrall oiiice location directs the closure of the particular crosspoint connection. Upon the closure of this crosspoint connection, the second series of pulses continuously present on the link terminals are directed therethrough to inhibit the loop scanning means. Accordingly, the absence of subsequent double-meaning service-request indications with respect to a particular substation is indicative of the proper closure of a crosspoint connection for the establishment of a communication connection thereto. Therefore, the signal developed by the loop scanA ing means provides an indication for a servicerequest condition and a crosspoint failure condition, suvra, in addition to indicating by the absence thereofl a compliance with a crosspoint closure order from the central odice in the case of originating calls.

The manner of monitoring the proper closure of a particular crosspoint connection in the case or" a terminating call differs in that the indication generated is identical to that generated to indicate a hang-up change condition. Prior to the central otce location directing,T a closure of a particular crosspoin-t connection to eiect a corn- .iunication connection, the system conditions are such that the rst series of pulses are absent from the link ter- 4minal connected to the particular crosspoint connection in the switching network. However, the immediate state condition of the called substation is necessarily one of onhook `and the transmission gate associated therewith allows the appearance of the first series of pulses at the loop terminals of the switching network. Therefore, following a crosspoint closure in the case oi' a terminating call, the link scanning means becomes responsive to me rst series of pulses which now appear through the closed crosspoint connection at the link terminal connected thereto. The appearance following an absence of the first series of pulses at the connected link terminal is recognized by the link scanning means jointly with the memory' circuit means, which attest to lthe prior absence thereofy to develop a double-meaning hang-up change condition indication. Therefore, the signal developed by the super-- visory system upon the appearance following the absence ofthe first series of pulses at the link terminal of the switching network indicates a hang-up change condition if a communication connection has been effected as well as a proper closure of a particular crosspoint if such connection is to be effected for a terminating call to a sub- Y station.

The last change condition in the operation of a substation for either an originating or a terminating call is that of hang-up whereupon the crosspoint connection is directed to release. Conversely with respect to the monitoring of a crosspoint closure in the case of a terminating call, the monitoring of a proper crosspoint release is effected subsequent to the proper central oiice action by the recognition of the absence following the appearance of the iirst series of pulses by the link scanning means and the memory circuit means to generate a double-meaning answer-change condition indication. Therefore, the signal developed by the system upon the `absence following the appearance of the first series of pulses at the link terminals of the `switching network indicates an answer change condition if a communication connection has been established `as well as a proper release of a crosspoint connection if such connection is to be disconnected subsequent to the receipt of a resolved hang-up change condition indication. The ambiguities inherent in these signals as generated are resolved at the central office location by the `above-mentioned features relating to memory circuits operative to distinguish the proper sequence of signals to be expected in both the progress of a call and also in response to a proper function of the switching network.

Accordingly, the features of this invention so far described provide supervisory intelligence to the central oilice in the form of change condition information, as distinguished from state condition information, relating to a particular substation being served as well as monitoring information of the proper operation of the crosspoint connections comprising the remote switching network. The randomness and low average rate of occurrence of the appearances of such information allow for the provision of a fur-ther feature of this invention which relates to the employment of phantom circuitsl as signaling paths over the communication links with a minimum of resultant interfering tones. The information which is transmitted over these phantom circuits operates appropriate indicating devices at the central oilice common to all of the served substations on a time basis for directly indicating the particular change condition of a substation to initiate appropriate action bythe central office equipment. The presence of each indication at the central office provides a flag indication (i. e., a signal indicative of the presence of supervisory information in a specific component circuit) to the common control unit thereof to initiate a sampling of each indicating device to resolve the information contained therein according to the state condition of the communication connection.

These and other features of the invention ywill be better understood upon consideration of the following description taken in conjunction with the accompanying drawings in which:

FGS. l, 2 and 3 are general circuit representations of a supervisory circuit embodying the principles of this invention and adapted for the transmission of intelligence indicative of the particular change conditions of a plurality of substations provided service in a line concentrator telephone system. FIGS. l and 2 show the line concentrating portion of the telephone system which is remotely located from a central oiiice location shown in FIG. 3. FIGS. l, 2 and 3 are arranged together as shown in the key diagram of FIG. 8;

FlGS. 4(61) and 4(b) are time diagrams which illustrate the appearances of the P1 and P2 pulses at the loop terminals of a remotely located switching network to be detected by a loop scanning meansV during the progress of an originating call and a terminating call, respectively;

FIGS. 5(a) and 5(b) are time diagrams which illustrate the 'appearances of the Pil pulses at the link terminals of the same remotely located switching network to be detected by a link scanning means during the progress of van originating call and a terminating call, respectively;

FRG. 6 is a time diagram keyed to iFIGS. 4 and 5 which illustrates the progress of both an originating call .and a terminating call as recorded in the route memory of a common contnol unit at the centnal oiice location; and

FIG. 7 is a diagram which illustrates the timing sefquenoe employed bythe common control unit at the central office location to distinguish a random disturbance, a flash or alert condition, and a true hang-up.

Referring to FIGS. l, 2=and 3, a line concentrator telephone system is shown which is adapted to serve a group of substati'ons Sii() through S59 over ten communication iinks L0 through L9 emanating from a central office |location to provide a siX-to-:one concentration. While the illustrative-embodiment provides service to 60 substatiOnS, it is -to be understood that the number of served substations may vary depending upon estimated traic conditions with respect thereto. {[n addition, it is to be understood that one of the substations Slt through S59 may represent a group of substations provided with party line senvice in a manner well knovm in the art. The equipment lwhich is shown in FGS l and 2 is 1ocated remotely from the central ollice location shown in FIG. 3 and comprises that apparatus associated With the function of concentrating traiic from the substations S00 through S59 over the links L0 through L9. It is to be further understood that a plurality of line concentrator units such as depicted in EFIGS. l yand 2 or a multiple concentration of served substations may be employed with `a single central oice location without deviating from the concepts of this invent-ion.

lCommunication connections are provided between the substations S00' through S59 :and the central otiice location shown in FIG. 3 thuough the links L@ through L9 which are 4selectively connectable Vto particular ones of the substations through the agency of the switching netwlork 1 of the line concentrator unit as controlled by the central oliice location. The manner in which the switching network 1 is controlled by the central office location does not constitute a pant :of the present invention. There are numerous examples in the present art of apparatus for affecting a control of the switching network of a line concentrator unit from the central oiiice location. To simplify iand particularly direct the descriptron of the present invention, the switching network 11 is shown skeletonized to depict only the terminals thereof. Y It should be understood, however, that the switching network 1 may Vcomprise such elements that are operative to complete a communication connection therethrough. Examples of such elements lare -two or threeterminal semiconductor devices, gaseous devices, crossbar switching devices, relay devices, etc., which are adapted to open or close a communication connection.

in the arrangement as shown, each of the substations S00 through S59V is connected to the central office location of FIG. 3 through alternating-current coupling networks in la manner well known in the A communication path between a particular substation, e.g., S59, and the central :office is established from the repeating coil or tnansformer 3;V of substation S59, the dual primary of which is connected to the subset thereof through a pair of `wires 5, through a preselected crosspoint connection in the switching `network 1 to a repeating coil 7 associated with a preselected one of the links L@ through L9 and along the preselected link to the central oce location. An unbalanced switching operation is performed by the switching network l ,in selectively connecting the substation S59 to 1an idle one of the trunks L@ through L9. The ground connection provided to the secondary of the repeating coil 3 and the primary of the re eating coil 7 establishes a gnound return and creates in that portion or the communication path an unbalanced connection. However, the repeating coil 7 recreates a fully balanced system for the remaining portion or" the communication path to the central office location of FdG. 3. -It should be evident that the present invention is similarly applicable to systems wherein a balanced switching operaion is utilized.

An unbalanced switching method is employed in the illustrative embodiment of this invention wherein a single crosspont is closed in the switching network `l to provide a communication path from a particular one of the substations Sil@ through S59 through a selected one of the links Lil through L9. An advantage which can be secured by the employment of an unbalanced switching scheme is that only la single crosspoint need be provided and o erated to establish a communication path between a particular substation and the central office location. Further, the switching network l `is essentially self-contained and conductively isolated from currents induced from power lines and other sources oi interference. Further, the repeating coils provide balanced termination for each communication path which effectively cancel longitudinal currents thus reducing noise impairment or" speech signals. However, a disadvantage inherent in such schemes is that there is no direct-current connection established `upon crosspoint closure between the particular substation and the central ollice location. In present day telephone systems, whether of the type employing line concentra-tor units or not, the supervision of served substations -is elected by 'a sampling of the line current condition of a particular substation to determine the immediate state condition thereof. For example, the supervisory systems employed in present day line concentrator telephone systems operate to detect servicerequest conditions at the remote location :on a time basis and, once fa communication connection has been established to the substation, further supervision is effected at the centrall olce location on a direct-current basis along the interconnecting link for the determination of both ion-hook and oil-hook state conditions thereof to be processed for the determination of the actual change condition of the substation. As mentioned above, this invention contemplates no supervision whatsoever at the central cnice location of the immediate state condition of the substations S96 through S59 but, rather, conte. plates the transmission to the central oiice location from the remote location supervisory information indicative of the actual change condi-tion in the operation of a substation.

The substation equipment with which `the present supervisory system may be employed is showin as being of a conventional type and well known in the art. The battery Bl is connected through the resistor 9, through one primary of the repeating coil 3, through the individual subset along the pair of wires in which is serially included the ilash device FD and thererorn through the second primary of the repeating coil 3 and the resistor lll to ground. A capacitor 13 is interposed between the dual primaries of the repeating coil 3 to provide a `luy-pass for alternating-current signals of the resistors 9 and il of the battery feed circuit while avoiding a shunt thereacross to direct-current iiow by providing a high impedance thereto. The telephone subset included in the substations Sd@ through S59 operates conventionally to prese-nt a high impedance to loop current llow when 10 in an on-h-ook condition and a low impedance thereto when in `an off-hook condition.

Connected in parallel across the capacitor 13l is a voltage sensitive transmission gate which is illustrated in comprising a diode l@ which is connected in parallel with the capacitor l through the resistors l5 and l?. The diode 'i9 may preferably be of the type commonly referred to as a Zener diode or a conventional diode in combination ywith appropriate biasing means. The voltage conditions within the substation loop` are such that during the on-hook condition of a particular substation, eg., substation S59, there is low current flow through the substation loop causi-nsy a potential to appear across the capacitor T13 which is suilcient to maintain the diode i9 in a low impedance condition. However, an Off-hook condition caused by the removal of the receiver at substation S59 results in anrincrease in the substation loop current supplied from battery Bl. through the now low impedance provided by the subset thereto. The resultant decrease .in the voltage developed across the capacitor 13 and the diode l@ upon the substation S59 entering into an cil-hook state condition is below the breakdown potential of the diode i9. Accordingly, it is evident that the vimpedance presented by the diode Il? is determined by the `current condition in the substation loop and is evidential of the immediate state conditi-on of the substation S The dash device PD is, however, operative to provide an open loop condition for substation S59 for a predetermined time interval during an ofi-hook state condition thereof to generate a flash or alert condition indication as is hereinalter described.

series ci pulses, hereinafter referred to as Pl pulses, is directed from an oscillator 23 through the capacitor 2l, to the cathode of' the diode lil, the anode O which is connected through the capacitor .f1/7 to a point A. An individual point A is provided for each of the substatious through S59 to provide a sampling point for each of the loop terminals Vil@ through V59, respectively, of the switching network l for the loop scanner 2% whi i is connected thereto. Point A is also connected to the ungrounded side of the secondaries of the repeating coil L= associated with each of the substations Sti() thmugh Sd through the capacitor S. Accordingly', the P1 pulses from source Z3 appearing through the :diode 19 during an ori-hook state condition of the associated substation also appear on the unbalanced portion of the communication path. The ungrounded terminals of the repeating coils 3 are conested directly to the loop termina-ls Voll through J5- ol' the switching network l which correspond to the` substations Still through S59, respectively.

A second series of pulses, hereinafter referred to as P2, pulses, is provided by the source 23 through a phase shiter 3l and is coupled through the amplifying devices to all ten of the link Iterinn'hals Htl through H9 of the switching network l. A battery B2 is also connected t0 each or" the link terminals Htl through H9 of the switching network l through the amplifying devices 33 to supply hold current to each of the crosspoint connections to maintain them in a conductive state once operated. Accordingly, crosspoint holding power is supplied locally which allows the crosspoint current to be independent 0f substation current. ln such cases, the crosspoint element has a conductive state controlled by the central oiiice location but maintained by current locally supplied. The amplifying devices 33 serve as butter elements to provide high impedance alternating-current paths to the battery B2 feed circuit to minimize crosstalk between and shunt transmission loss through communication paths in the switching network 1. A link scanner 35 is connected to each of the link terminals Htl through H9 of the switching network l through capacitors 37 and is operative to scan each link terminal on a one-out-of-ten basis.

Accordingly, the loop terminals V09 through V59 and the i nk ltern'iinals Htl through H9 of the switching network .l are continuously sampled by the loop scanner 29 and the link scanner 35 on a time basis for the presence of the P1 or P2 pulses Vand for the presence of the P1 pulses, respectively. The loop and link scanners 29 and 35, respectively, are stepped synchronously by the units counter 39 which is responsive to advance pulses directed from the 4common control unit 10%` at the central office location. While the common control unit 106 is shown in block form, it may be of the type las substantially set forth in the copending patent application of W. A. Budlong et al., Serial No. 688,386 filed October 7, 1957 now Patent No. 2,955,165 issued October 4, 1960i. Contained within the common control unit 19? are counting means (not shown) synchronously operated with respect to unit counter 39 and the tens counter `41, infra, to indicate the count condition thereof at the control office location in a manner hereinafter to 'be described.

An advance pulse is directed from the central office establishment of a communication connection therethrough to a particular substation. It should be evident that a pair of different superaudible frequencies may be employed instead of the P11 and P2 pulses if appropriate filtering and comparison devices are employed to duplicate the function of the coincidence gating arrangement now to be described.

The loop scanner 29 hereinabove described is operative to conduct the P1 and P2 pulses from oscillator 23 and phase shifter 51, respectively, upon their appearance at the particular loop terminals V through V59 of the switching network 1 being sampled. As mentioned above,

. the loop scanner 29 is responsive to the P1 pulses conin a manner hereinafter to be described along a conducg tor 43 `and through a delay network 46 -to step the units counter 39. The units counter 321 and a tens counter 4,1 are adapted to have a combined operation for counting 60 ladvance pulses in a l0 6 fashion. The units counter 39 recycles upon the application thereto of ten advance pulses, each cyclic operation thereof being effective to step the tens counter 41 which comprises six stages. The loop scanner 29, in response to the counters 39 and 41, sca-ns `for the presence of the P1 or P2 pulses at the loop terminals Vtltl through V59 of the switching network -1 corresponding to the substations S90 through S59, re-

' spectively. The substation-s Stt through S59 are convcniently divided into six groups of ten substations. To effect a scanning on a one-out-of-() basis, the loop scanner 29 is adapted for a 10 6 operation and is controlled by the counters 39 and 41 to determine the particular group and individual substation which is to be scanned, respectively. The units counter 39', however, operates singly to control the operation of the link scanner in scanning on a one-out-o-f-ten basis the ten link terminals H0k through H9 of the switching network .1 for the appearance Vof the P1 pulses thereat. rIlle loop and link scanners 29 and 35, respectively, may be of a type well known in the art land a detailed description thereof is not deemed necessary.

Accordingly, the scanning is provided by the loop scanner 29 andthe link scanne-r 35 for appearance of either P1 or P2 pulses at loop terminals V {it} through V59 and the P1 pulses at the link terminals He through H9, respectively. The loop scanner 29 operates to scan each of the loop terminals Vtt through V59 on a one-out-of- 60 basis and the link scanner 35 operates to scan the link terminals Htl through H9 on a one-out-of-ten basis. Fromthe description so far evolved, it is obvious that the link scanner 35 completes six scanning cycles for each scanning cycle of the loop scanner 29. The benefits which may be derived from such operation will be discussed hereinafter with respect to a flash or alert condition, the detection of which is had by `a scanning of the link termin-als rather than the loop terminals of the switching network 1 -due to time requirements imposed by a sequential scanning of the substations Stili-S59 and lirnitations imposed upon 4the frequencies of the advance pulses which may be employed therefor due to loaded cable transmission characteristics.

At this point, it might be mentioned that the repetition frequency of the P1 and the P2 pulses developed by the source `oscillator 23 is superaudible and of the order of twenty kilocycles in one illustrative embodiment. The pulses P1 and P2 are time displaced with respect to cach other by the phase shifter or delay 31; in one illustrative embodiment the delay was one-half of a cycle. The choice of a superaudible frequency for the monitoring is desirable as there is a continuous appearance of such pulses throughout the system. For example, the P2 pulses appear continuously on the link terminals HO through H9 of the switching network 1 even during the ducted through the diode 19 when in a low impedance condition during yan on-hook condition `of the substation S59 and, similarly, to the P2 pulses directed through a closed connection in the switching network 1. A coincidence gating arrangement is connected through an amplitier 49 to the output of the loop scanner 29 and cornprises the AND gates 45 and 47 to which the pulse sources 23 and 31 are respectively connected as reference pulses to sensitize the supervisory system only to generated pulses.

During the on-hook state condition of the substation S59, the diode 19- is conductive and the loop scanner Z9, when interrogating the loop terminal V59 associated therewith, detects the P1 pulses which are thereupon directed therethrough to the `amplifier @9. ri'he output of the amplifier 49 is connected to an input of each of the AND gates 45 and 47. The other input of the AND gates 45 `and 47 are connected to the source 23 and phase shifter 31, respectively. AND gates of this type are well known in the art and operate such that an output pulse is directed therefrom only on the simultaneous appearance of pulses on both input leads. It is evident that each time one ofthe P1 pulses is transmitted through theY diode 19 to appear at the loop terminal V59 and through the loop scanner 29 at one input of AND gate 45, the AND gate is coincidently enabled due to the appearance of a pulse at the second input thereof from the pulse source 23. Accordingly, a signal will be directed through the AND gate 45 upon each appearance of a P1 pulse through the diode 19 at the loop terminal V59 each time a sampling thereof is effected by the loop scanner 29 during an on-hook state condition of substation S59. The output of the AND gate 45 and similarly the output of the AND gate 47 are connected to first and second ones -of the inputs ofthe OR gate 50, respectively. The output of the OR gate 5d is connected to the detector 51 which is operative to develop a direct-current characteristic indication of the appearance of either the P1 or the P2 pulses at point A. The output of the detector 51 is connected to -a logical inverter circuit Si?, of =a type well known i-n the art, which operates to produce an output signal opposite to that of the input signal. Accordingly, only upon the `absence of a pulse at the output of the detector v51, which corresponds to an absence of both P1 and P2 pulses at the loop terminal V59 indicating an off-hook state condition of substation S59 and the `absence of a connection between loop terminal V59 and any link terminal within the switching network 1, is a pulse directed by the inverter circuit 53 to one of the inputs of the A-ND gate 55, the second input of which is connected to the conductor 43 upon which the `adv-ance pulses appear.

The function of the delay network 46 interconnected between the conductor 43 and the units counter 39 now becomes obvious. the AND gate 55 `slightly precede the application of the advance pulse to the counter 39 which controls the loop scanner 29, the link scanner 35 and the memory scanner 57, to be described hereinafter, due to the finite time interval required by the detector 51 to normalize in response to either the receipt or Iabsence of the P1 and P2 pulses at the point A. The loop scanner 29' may advantageously be adapted to be positioned one step in advance it is necessary that the enabling ofV after defined, of FIG. 4; the simultaneous absence thereof subsequent Vto the point CPR indicating a subsequent service-request change condition. As the record of the progress of the call is maintained in the common control i?, as described hereinafter, an indication to the central ofce location from the signal pulse transmitter 59 prior `to the proper release of a crosspoint connection can be distinguished as a crosspoint failure. The signals transmitted lto indicate a service-request `change condition and a crosspoint failure are identical save for the occurrence thereof with respect to expected change conditions. Though ambiguity exists, a :distinction is made between service-request change condition and crosspoint failure indications in :the `common control unit Miti at the central office location, as is hereinafter described.

The loop scanner functions solely to detect the service-request change condition of the substations Sti-il through S59 and false openings of those crosspoint connections through which service is provided thereto; the signal being developed thereby being hereinafter referred to as an Sli/CPF signal, i.e., a service-request crosspoint failure signal. All further change conditions which are attributable to the substations Sil-ii through S59 are detected through the agency of the link scanner '35' which senses the presence of only Pl pulses on the link terminal connections Hb through H9 of the switching network l at the point B. The output of the link scanner is connected to the amplier d@ which is, in turn, connected to one of the inputs oi the AND gate 63. A second input of the AND gate e3 is connected to the source 23 so as to provide a coincidence gating thereof by the P1 pulses in the manner described with respect to the AND gate d5. The link scanner 35 and associated circuitry are, accordingly, adapted to sense only for P pulses, as the AND gate 63 is gated solely by the Pi pulses from source 123 and is not affected by the P2 pulses from phase shifter 3l. The output of the AND gate 63 is connected to the detector circuit 65, the output of which is directed to one of three inputs of the AND gate 67. It is evident that, as described above, during an oit-hook state condition of substation S59, P1 pulses do not appear at the link terminal Htl of the switching network l through the now closed crosspoint connection and there is no output 'from the detector 65. Although the P2 pulses are being detected at 'this time by the loop scanner 2% at point A of the loop terminal V59 and appear on the link terminal Htl, they are effectively blocked by the coincidence gating requirement of the AND gate d3, i.e., PIL pulses. A second of the input terminals of the AND gate 67 is connected to the conductor i3 so as to be enabled, in a .manner described above with respect to the operation of the loop scanner 29 and AND gate 55, sliGhtly in advance of the stepping of the link scanner 35. The third 'terminal of the AND gate 67 is controlled in a manner 'to indicate the prior state condition of each of the links L0 through L9 as to the presence of the Pl pulses at the link terminals Htl through H9, respectively, as deter mined by the immediately preceding sampling thereof by the link scanner 35, hereinafter described.

Accordingly, to two of the input terminals of the AND gate 67 are directed characteristic indications of the :immediate state condition and the prior state condition of the particular one of links Lil through L9 along which n communication connection is provided through a now `closed crosspoint and to the other input thereof is di- :rected an advance pulse from conductor d5 to effect a :comparison oi those signals in proper time sequence.

The control of the third terminal of the AND gate 67 vis effected by the link memory unit 69 comprising memory units Mt) through M9. The memory units Md through M9 correspond individually to the links Lt) through L9, respectively, and are operative to record the state condition thereof with respect to the presence of P1 pulses ras determined by the link scanner 355 and associated logic circuitry, hereinafter described. The memory units through M9 may advantageously comprise bistable devices, i.e., magnetic cores, flip-lop circuits, etc., in which may be recorded information,indicating the two possible state conditions of each of the links Lil through L9, i.e., Pl pulses present or absent. The memory units Mil through M9 are each adapted to be sarnpied in a non-destructive manner, i.e., he state of operation thereof is'not disturbed by the link memory scanner or scanning selector 57 which is synchronously stepped with the link scanner 35 by the units counter Accordingly, each time the immediate state condition of one of the links Lil through L9 is sampled by the link scanner 35 and an indication thereof directed to the second terminal of AND gate 67, an indication of the prior state condition thereof is applied to the third input terminal of the AND gate 67 in a manner now to be described.

Prior to the generation of an expected hang-up change condition indication in the case of both originating and terminating calls, it is necessary that the substation be in an ori-hook state condition and the crosspoint connection associated providing communication connection thereto be closed. Conversely, prior to the gen-eration of an expected answer change condition indication in the case of terminating calls, it is necessary that the substation S59 be in an on-hook state condition and the crosspoint connection associated therewith be similarly closed. lt is evident that a closure of the crosspoint in switching network l precedes the answer change condition in order to apply ringing signals to the substation. As the crosspoint is closed prior to each of these change conditions, the appearance of the Pi pulses on the 'link terminals Hh through H9 oi the switching network 1, as controlled by the diode 3 9, occurs only during such time that the substation S59 is in an on-hook state condition which precedes an answer change condition. This is shown graphically in the time diagram of FIG. 5. Conversely, the absence of the P1 pulses at the link terminals Htl through H9 of the switching network 1 can only occur during an off-hook condition of the substation S59 which necessarily precedes a hang-up change condition.

Accordingly, as the crosspoint connection through which a communication connection is provided to the particular one of the substations Sti@ through S59 is necessarily closed during each of these change conditions, it functions as a memory device to eiectively distinguish an answer change condition and a service-request condition of a particular one of substations S09 through For example, it is evident that the oil-hook state condition of the substation S59 is common to and initiates both a service-request change condition and an answer change condition thereof. The crosspoint connection, accordingly, serves as a bistable memory device to distinguish therebetween by controlling the application of the Pi and the P2 pulses through the switching network 1 to inhibit the generation of an answer change condition indication prior to and a servicerequest change condition indication subsequent to a proper crosspoint closure. As the prior state condition ot each one oi the links Lt) through L9 as determined by previous sampling of the particular link is stored in the link memory 69, a detection of a change in the absence to the appearance of Pl pulses and, conversely, from the appearance to the absence of Pi pulses, by the link scanner 35 and associated elements cooperative there with can be interpreted logically as a hang-up change condition and an answer change condition, respectively, in a manner now to be described, such detection being subsequent to the proper closure of a particular crosspoint connection.

In the generation of a hang-up change condition indication, an appropriate crosspoint connection has been closed and the substation S59 has been in an off-hook condition precluding the presence of Pl pulses at the link terminal Htl of the switchingV network ll. Upon a return of the substation S59 to an ori-hook state condition, the resultant biasing of the diode i9 allows for the passage of the P1 pulses through the still closed crosspoint connection t the link scanner 35. The Pl pulses are now directe through the link scanner 35, ampliiier and the ANS gate 63; a characteristic indication thereof being developed by the detector 65 and applied to the second input terminal of the AND gate 67. Consider now the eiicct oi the memory unit Mtl associated with the link L@ to which the substation S59 has been connected through the closed cross-point connection. Prior to the return oi the substation S59 to the on-hook state condition, the state condition of link L@ connected thereto was recorded as having Pl pulses absent at the link terminal Htl by a non-readable indication in tbe memory unit Mil oi the link memory 69. The absence of a readable indication in the memory unit M@ is the normal condition thereof in the case of an originating call or, in the case of a terminating call, has been caused by the resetting oi the memory unit by a previously occurring answer change condition indication. The scanning selector 57 which is operated synchronously with the link scanner 35' senses the stored information bit in the memory unit Mil and directs an indication thereof to an amplifier 7l. The absence of readable condition in the memory unit Mtl is indicated through the amplier 7i and the delay network 73 at the point C. Due to the peculiar operation oi the inverter circuit 73, an absence of an indication at the point C provides an opposite or a positive characteristic indication to the third input of the AND circuit 6. Accordingly, in the hangup change condition, and the three input terminals to the AND circuit d'7 are provided with enabling voltages, ie., the advance pulse along the conductor 43, the output of the detector in response to the Pl pulses applied thereto through the link scanner 35 indicating a return to an on-hook state condition oi substation 85g, and the positive characteristic indication at the output of inverter circuit 7&3 due to the absence ot a readable indication in the memory unit Mil indicating a previous absence of the Pl pulses on the link Lt?. The AND gate 67 thereupon directs a pulse along the conductor Sl to the signal pulse transmitter 83 upon the appearance of the advance pulse along the conductor 43; the pulse from transmitter 83 can be resolved as a hang-up change condition of the substation S59 at the central oiiice location.

in a similar manner, the answer change condition in the case of a terminating call, is indicated by the AND circuit 77. The crosspoint connection prior to an answer change condition is necessarily closed for the application of ringing signals to the substation S69. However, the state condition of the substation S59 is onhook so that Pl pulses passed by diode l@ are detected through the crosspoint connection by the link scanner 3S. Upon substation S59 entering into an answer change condition, the ofi-hook condition of this receiver causes a biasing or" the diode l@ such that Pl pulses are not directed therethrough and through the crosspoint for detection by the link scanne Accordingly, an absence iollowing an appearance of Pl pulses through the switching network l provides for an absence of directcurrent potential from the detector so that the AND gate 67 is not enabled. The output of the detector do' is, however, connected to the AND gate 77 through the inverter circuit 7%; AND gate i7 is, therefore, supplied a positive characteristic indication oi the absence of the direct-current potential at the output of the detector 6:5'. The AND gate '".l is further controlled by the memory unit Mb. The state condition of the link L@ prior to the removal of the receiver at substation S59 was such that Pl pulses had been appearing thereon, as indicated by a readable indication stored in the memory unit Md. Accordingly, the three input terminals of the AND gate 77 are provided with enabling voltages, ie., the advance pulse along the conductor 53, the output of the inverter Cil 79 in response to the absence of Fl pulses applied through the closed crosspoint connection, which functions as a memory device, and through link scanner 35 indicating an oit-hook state condition of the substation S59, and the presence of a readable condition in the associated memory unit Mtl indicating a previous state condition of the link Lb during which Pl pulses were present. Accordingly, the AND gate 77 is now operative to direct a pulse along the conductor 5 to the signal pulse transmitter S3 upon the appearance of an advance pulse along the conductor 43; this pulse from transmitter 83 can be resolved as an answer change condition of the substation S59 at the central oiice location.

Making specic reference to the time diagrams of FiG. 5, it is evident that the appearance of the Pl pulses at the link terminal Ht) precedes an answer change condition in the case of a terminating call and succeeds a hangup change condition in the case of both originating and terminating calls. The appearance of the P1 pulses at the link terminal H0 preceding an answer change condition commences upon the closure of a crosspoint connection due to the then on-hook state condition of the substation S59. The memory units Mtl through M9 are each adapted to be set or reset by a hang-up change condition or an answer change condition indication, respectively, peculiar to that substation provided a communication connection along the links L@ through L9, respectively. As is hereinafter described, the system conditions which result from the closure and release of a crosspoint connection to a substation in an on-hook state condition and the information necessarily stored in the memory units Mtl through M9 are such as to enable the AND gates 67 and 77, respectively. Accordingly, upon the appearance of an advance pulse along the conductor 43, an output signal is developed by an. enabled AND gate 67 or '77. Thus, the output signal indications of the AND gates 67 and 77" have a dual or ambiguous significance. As the output of the AND gate o7 indicates either a hang-up change condition or a crosspoint closure to a substation in an ori-hook state condition, i.e., for a terminating call, the output signal will hereinafter be referred to as an HU/CPC signal. Similarly, as the output of the AND gate 7'7 indicates either an answer change condition or a crosspoint release, the output signal from gate 77 will hereinafter be referred to as an ANS/CPR signal.

The Htl/CPC and ANS/CPR signals are employed to monitor proper operation of the crosspoint connection, as further described hereinafter, upon a resolution of that ambiguity at the central oiiice location. However, these signals are similarly operative to atleet the memory units Mb through M9 to provide an indication of the presence or absence of Pl pulses at the link terminals Htl through Hi For example, in the case of an originating call, as illustrated in the time diagrams of PEG. 5 (a the Pl pulses appear only subsequent to a hang-up change condition whereupon the memory unit Ml? is set by the HU/CPC signal through the amplifier S7 to provide a readable indication upon a subsequent sampling thereof by the scanning selector 57. Accordingly, a subsequent absence of Pl pulses at the link terminal Hl) affects the inverter 79 such that the AND gate 77 is enabled to develop an ANS/CPR signal upon the appearance of an advance pulse on conductor i3 which can be resolved at the central cnice location as indicating a proper crosspoint release. Similarly, the ANS/CPR signal generated upon a crosspoint release is operative to reset and normalize the memory unit Mi? through the amplier S6 to provide a nonreadable condition therein.

ln the case oi a terminating call, as illustrated in time diagram of FlG. 5 (b), the HU/CC signal generated upon a crosspoint closure due to a non-readable condition in the memory unit Mtl and the resultant appearance of P1 pulses at the link terminal Htl is operative to set the memory unit M@ through the ampliier S7 to provide a readable condition therein indicating the presence of P1 19 pul es at the link terminal H0. A subsequent answer change condition of the substation S59 and the resultant absence of the P1 pulses at the link terminal Hit results,

due to a readable condition in the memory unit Md, in the enabling oi' the AND gate 77 upon the appearance of an advance pulse along conductor 43 and the generation of an ANS/CPR signal. The ANS/CPR signal again resets the memory unit M to provide a non-readable condition therein indicating the absence of P1 pulses at the link terminal H6, whereupon the reappearance thereof results in the enabling of AND gate 67 to generate an HU/ CPC signal indicative of a hang-up change condition of substation S59. The HU/CPC signal and the subsequent ANS/ CPR signal electively set and reset the memory unit M0, respectively, in an identical manner as described for the case of an originating call. Accordingly, the memory unit is normalized upon the completion of both an originating and a terminating call to substation S59. The readable condition to which each of the memory units M0 through M9 is set provides a store for the prior state condition of the individual links L0 through L9 with respect to the presence of the P1 pulses at the link terminals H0 through H9 of the switching network 1. Again referring to the time diagrams of FIG. 5, it is evident that a readable indication is only contained in the memory unit M9 during those intervals corresponding to the lined areas indicated between CPC, the closure of the crosspoint connection, and ANS, the answer change condition of substation S59, in the case of a terminating call and between HU, the hang-up change condition, and the CPR, release of the crosspoint connection, for both originating and terminating calls.

The HU/CPC signals and the ANS/CPR signals thus developedby the AND gates 67 and '77, respectively, have a dual or ambiguous significance which relates to the changeconditions of both the particular one of substations S60 through S59 being served and the crosspoint connection through which service is provided thereto. Such ambiguities are resolved at the central oce location according tothe time relationship of the reception of each 0f the HU/CPC signals and the ANS/ CPR signals with respect to the normal sequence of the progress of state conditions of a communication connection. A record is maintained at the central office location on a link basis of the identity of the particular substation being served on a particular one of the link L0 through L9 in a route memory contained in the common control unit 100. The route memory may advantageously be a barrier grid storage device of the type described in the above-identied A. E. Budlong et al. application or in the Bell System Technical Journal of November 1955 on pages 1241-1264. Upon a service-request change condition having been received and the particular substation, i.e., substation S59, identified, an idle one of the links L0 through L9 is selected and the identity of substation S59 is written into a group of memory spots associated with the selected link in the route memory of the common control unit 16d. Accordingly, subsequent change condition indications which are received and identified on a link basis are attributed to substation S59 or the crosspoint connection through which communication connection is provided thereto along that one of the links Lil through L9. The identity of the substation is only erased upon the reception of an ANS/CPR signal indicating a release of the crosspoint connection.

The HU/ CPC and ANS/ CPR signals providing supervisory information of the crosspoint connection occur subsequent to a control thereof by the central oiiice location as a result of the change in system conditions accompanying such control, as described above. Accordingly, the ambiguity which exists with respect to the HU/ CPC and ANS/CPR signals directed to the central oice location from the signal pulse transmit-ter S3 can be resolved thereat laccording to the time sequence of appearance of these indications. To resolve the ambiguities inherent in the I-lU/CPC and ANS/ CPR signals, a record is simultaneously maintained in the route memory of the common control unit lil@ at the central office location of the state of the communication connection to the substation S59 with respect to link Lil, i.e., the communication connection is to be eiected; the communication connection has been effected; the communication connection is to be disconnected; or the particular link is idle. No information is recorded at the central oiice location peculiar to the substation S59 during an idle state condi-tion thereof. it becomes evident that, in the case of `a terminating call, if an HU/ CPC signal is received at the central office location which is identiiied as peculiar to link L0 at a time when the route memory of the common control indicates that a communication connection is to be effected to the substation S59, the central olice location resolves this signal to indicate a proper closure of the crosspoint to provide a communication connection thereto. However, if an HU/CPC signal identified as peculiar lto link L@ is received at a time when the route memory of the common control unit indicates that such link is idle, the central oice location is able to resolve this signal to indicate an improper or false closure of a crosspoint connection. With respect to the monitoring of a proper closure of a crosspoint connection in the case of an originating call, Vas was hereinabove described, the absence of subsequent SR/ CPF signals to the central oice location upon the ordering of a crosspoint connection to close is indicative of the presence of P2 pulses through the switching network 1 to the loop scanner 29l which presupposes the closure thereof. Accordingly, the ambiguity inherent in the HU/ CPC signal is resolved according to the appearance thereof at the central otiice location with respect to the state of the communication connection recorded in the route memory of the common control unit 100. If the communication connection has been effected, the HU/ CPC is resolved to indicate a hang-up change condition. Accordingly, a proper closure of a crosspoint connection is indicated for the establishment of an originating or a terminating call along a selected one of the links L0 through L9 by the `absence o-f subsequent SR/ CPF signals or by a HU/CPC signal, respectively, at the central office location. Moreover, a false or improper closure of a crosspoint connection is indicated by the appearance of a HU/CPC signal during that time in which the route memory of the common control unit 189 indicates that a communication connection is not to be established.

A monitoring can be effected of the proper release of the crosspoint connection by the central oice location. A crosspoint is directed, as the iinal action of the central oiiice location in serving an originating or fa terminating call, to release subsequent rto the reception of a HU/CPC signal which has been resolved 'as a hang-up indication.

' In a manner similar to the resolution of the ambiguity inherent in the HU/ CPC signal, the central ioice location is able to determine the positioning of an ANS/CPR indication 'with respect to the state of the communication connection as stored in the route memory of the common control unit 160. =If an ANS/CPR signal is received and identified las peculiar to link L0 while the route memory indicates that a communication connection has been effected between link Le and substation S59, the central oiiice Ilocation resolves the signal to indicate an answer change condition. However, if an ANS/ CPR signal, which is identied as peculiar to link Li?, is received lat a time when the route memory of the common control unit itin indicates that such connection is to be disconnected, the central ofce location is able to resolve this signal to indicate a proper crosspoint release. As has been described above, an improper release of a crosspoint connection is indicated by the appearance of a SR/CPF signal 'during that time in which the route memory of the common control unit indicates that -a communication connection has been established to the substation S59 and prior to the receipt of a HU/CPC signal indicating a hang-up change condition.

all"

Accordingly, three indications developed by the supervisory system of this invention provide for not only la notifica-tion directly to the central cnice location of the change conditions of the substation being served but also provide a monitoring of the crosspoint connection las mentioned above. The Sli/CPF indication serves to notify the central oilice location of a service-request change cou- -dition or of a mid-conversational crosspoint failure, the labsence of subsequent indications denoting a proper closure of a crosspoint connection for serving an originating call; the HU/CPC indication serves to notify the central Ioilce location of a hang-up change condition or of both an improper closure of a crosspoint connection during such ytime that a link connected thereto is not to be effected and `a proper closure of a crosspoiut for serving a Itermihating call; and the ANS/CPR indication serves -to notify the central oiiice location of an answer change condition or of the proper release of a crosspoint connection in response to orders received from the central olce. Also, the reception of the ANS/ CPR indication `with respect to a particular link during such time that a substation is not being served therealong serves to notify the central ofce location of 1a malfunction in the supervisory system, eg., non-synchronous operation `of nthe tens counter il and the units counter 39 with respect to corresponding counter units, not shown, contained in the common control unit The outputs of the AND gates d'7 and 7'7 are each connected through the conductors ell and 8:5' to respective ones of the two inputs of the signal pulse transmitter S3, respectively. The signal pulse transmitter 83 is operative to generate a pulse of predetermined polarity according to which of two inputsV thereof is enabled. The signal pulse transmitter 83 may be any type of well-lmown bipolar pulse transmitter from which is provided an output signal of predetermined polarity according to which one of two inputs is activated or more specifically, may be of the type disclosed in the copending l. Dorros patent application, Serial No. 824,433, filed on even date herewith. Upon the reception of an HU/CPC signal on conductor 81, the operation of the signal pulse transmitter 83 is such that a positive pulse is developed thereby. Upon the reception of an ANS/ CPR indication on the conductor S5, a negative signal is developed by the signal pulse transmitter 33. Accordingly, the positive and negative pulses developed by the signal pulse transmitter 83 and indicative of HU/ CPC and ANS/CPR signals, respectively, are distinguishable with respect to each other. The practicability of employing a bi'aolar signal pulse transmitter for the transmission of HU/CPC and Al'slS/Cil?` signals, respectively, is due to the fact that such signals cannot occur simultaneously with respect to a same iinl; as the dual significance of each ot these signals is correspondingly mutually exclusive. The output of the signal pulse transmitter 83 is connected through the repeating coil 8g to the links L@ and Ll in a phantom circuit arrangement.

Phantom circuits are well known in the art and provide means whereby an additional signaling channel may be provided over two existing communication connections. Such phantom circuits, for example, are described on page 204 of Communication Engineering, Third Edition by Everett and Annar. Accordingly, each terminal of the secondary winding of the repeating coil @d is connected to one of the midpoints oi the secondary windings of the repeating coils 7 associated with links L@ and Ll, each of which serves as a side circuit for the signaling channel established between the signal pulset transmitter S3 and the central oice location. Basically, the operation of the phantom circuit is such that currents directed from the secondary oi the repeating coil 89 divide equally from the midpoints of the secondary windings of the repeating coils 7 in links L@ and Ll and ilow in the same direction in the two wires comprising each, respectively. At the far end of the links L@ and Ll, the currents in each of the two wires produce equal and opposing magnetomotive forces in the primary windings of the repeating coil 9i associated therewith and so are effectively' canceled in the secondary windings thereof which are connected to the central ollce switching network, not shown. Connected at the midpoint of each of the primary windings of the repeating coils @l arranged in the links lati and Ll at the central office location is one terminal of the primary winding of repeating coil Accordingly, pulses developed by the signal pulse transmitter S3 and directed over the links Lil and Ll in a phantom arrangement are received at the primary windings of the repeating coil @3. t should be noted that a high degree of balance between the wires comprising each ot the linlrs Lil and Ll is not required for this application. in phantom circuits, in order to avoid interference between the individual communication paths and the phantom circuit which is superimposed thereon, a balancing ot the conductors comprising each communication path is desired to effect an equal distribution of current from the midpoint of repeating coil along each conductor. An imbalance of such conductors is productive of crosstall; or, in the case or" continuous signalug pulses in the audible range, an interfering tone. However, due to the randomness and relative inircquency oi the pulses developed by the signal pulse transmitter S3, an interfering tone will not appear. The pulses directed from the signal pulse transmitter 0S do cause a slight interference in the form oi random blips on the commtmication paths. However, to eliminate such blips would require balancing of the links which, for all practical purposes, is not necessarily warranted when comparing the cost of such balance with the slight annoyance caused by the transmission ot random signals over the superimposed phantom circuit.

Similarly, a phantom signaling circuit is provided for the signal pulse transmitter 59 and utilized for the transmission oi Sil/CPF indications to the central oflice location. The signal pulse transmitter di? is connected to the primary winding o the repeating coil 95. The terminals of the secondary winding of the repeating coil 515 are connected to the midpoints of the secondary windings oi the repeating coils 7 contained in the links lli; and L9, respectively. Accordingly, a second phantom signal circuit is established to the primary windings of the repeating coils @l contained in the links L8 and L9 at the central oilice location, the midpoints of which are connected to opposite terminals of the primary winding of the repeating coil 97.

The advance pulses which are generated in the common control unit 1G@ are directed to a signal pulse transmitter il? for transmission to the remote location. As the signals appear continuously, a separate signaling path is provided therefor between the repeating coil il@ 'located at the central ollce location and repeating coil i121 located at the remote location. The secondary of the repeating coil lil is connected to a signal pulse receiver E23 which is operative upon the receipt oi advance pulses thereto to direct an output signal along the conductor s3 to which it is connected.

The SFr/CPF signals, the HIJ/CPC signals and the ANS/CPR signals are directed along the phantom circuits superimopsed upon the links L@ and if and the links L@ and Ll, respectively, to the primary control unit Still at the central oice location through the secondary windings i the repeating coils 97" and 93, respectively. The secondary winding of the repeating coil 93 is connected to the bipolar signal pulse receiver 1&3 in the primary control unit lul which is operative to distinguish between the bipolar pulses wln'ch are representative of the l-lU/CPC signals and the ANS/ CPR signals, respectively. Similarly, the secondary winding of the repeating coil 97 is connected to the signal pulse receiver N5. The bipolar signal pulse receiver M3 is operative upon receipt of a positive signal or a negative signal through the repeating coil 93 thereto to direct an output to set the flip-hop devices 167 or lo?, respectively, to indicate the receipt of an HU/ CPC signal or an ANS/ CPR signal, respectively. Six ilarly, the signal pulse receiver MS is operative upon the 23 receipt of a signal through the repeating coil 97 to set the flip-flop device lll to indicate the receipt of an SR/ CPF signal.

Specifically, the flip-Hop devices lo?, and lill may be conventional type bistable multivibrator devices well known in the art which are adapted to assume one of two stable states of operation upon receipt of an input pulse thereto. The {lip-flop devices ltl', ltli and ill are normally reset. The output of each of the hip-liep devices 107, 109' and lill is multipled to the office scanne-r H3 and to the OR gate llS. The operation of the OR gate lll-.5 is such that a pulse is directed therefrom to the common unit lil-il upon a setting of any one of the lipilop devices 107, 199 or lll. Accordingly, it is only upon the `setting of one of the dip-flop devices i537, lil@ or lll due to -the appearance of a HU/CPC signal, an ANS/.CPR signal or a Sil/CPF signal, respectively, that an output is directed from the ORl gate i115 to provide a ilag condition alerting the common control unit lll@ to the presence of supervisory information in the primary control unit lul. The appearance of a flag condition in the primary control unit ldd operates t-o initiate a scanning of the outputs of the hip-flops N7, M9 and lll by the office scanner M3 under the con-trol of the common control unit 16S to provide a determination of which of the flip-flop devices i917, lil@ and lill has been set. it is evident that there is not a continuous scanning of the llip-ilop devices lll?, 109 and lll but that such scanning is only eifected during a time in which supervisory information is contained in the primary control unit lill.

At that time when a dag condition is received in the common control unit ltl through the OR gate i115, tranm-iss-ion of advance pulses to control the remote scanning is momentarily stopped until the supervisory information contained in the primary control unit ltll is resolved. The manner by which the advance pulses are transmitted to the remote location is hereinabove described. Accordingly, the supervisory information contained in the primary control unit lill cannot be mutilated by subsequently received supervisory information until identifica.- tion and resolution thereof has been effected in the manner now to be described. An identification of the supervisory information with lrespect -to a particular one of the substations Still through S59 and of the links Lo through L9 is provided by means of counter units, not shown, contained in the common control unit lill) which may be identical to the tens counter `4l and the units counter 39 shown in FIG. l. These counter units are accordingly adapted to provide identification on both a substation basis and on a link basis. For example, if a determination is made upon a scanning :of the outputs of the flip-Hop devices lil?, ltl and lll that the flip-flop device 111 is in a set condition indicating the receipt of a SR/ CPF signal, the common control unit Mill' can readily determine `on a substation basis the identity of the particular one of the substations Slltl throiigh S59 to which it is peculiar by referring to the count contained in both counter devices. However, it either of the ip-llop devices 167 or 1li? is determined as being in a set condition indica-ting the receipt of a HU/CPC signal or an ANS/ CPR signal, respectively, the common control unit lili) can readily determine on a link basis the identity of the particular one of the links L@ through L9 by referring to the counter contained therein corresponding t-o the units counter 39 of FlG. l. As the identit-y of the particular substation is recorded in the route memory of the common control unit f lll on a link basis, a correlation between the particular one of the links L through L9 as identified and the particular one of the substations Silit through S59 provided service therethrough is determinative of that substation which has undergone such change condition. As described above, not only is the identilication of the particular one of the substations Sh@ through S59 stored inthe route memory on a link basis but also appropriate memory spots are provided in which me contained the state condition of a communication connection. Accordingly, the receipt of a particular StR/CPF signal, HU/CPC signal or ANS/CPR signal and a comparison of such signal with the information of the state condition of the communication connection provided to a particular substation as recorded in the route memory of the common control unit 106 is effective to resolve the supervisory information indicated thereby in the manner which has been hereinabove described. Upon the receipt of a flag condition at the common control unit litll and the .subsequent identification of that one of the flip-flop devices lf, it?? and il'l which has been set, the set flip-flop device is thereupon reset by the common control unit itl-9 along the conductor 129.

In order to provide that a terminating call directed to the substation S59 may be transferred to another one of the remaining substations Silit through SSS when a customer group service is being provided by a line concentrator unit as shown in Fi vS. l and 2, the common control unit lll@ at the central oliice location is adapted to recognize a flash or alert condition from the substation S59; The flash or alert condition need not be indicated by a separate characteristic signal in itself but rather may comprise a resolved hang-up change condition indication followed within a predetermined interval of time by a resolved answer change condition indication both identified with the substation S59. More specifically, a flash or alert signal is indicated when an ANS/CPR signal is received at the central office location during that time when the route memory of the common control unit y indicates that the communication connection is to be disconnected as illustrated in FiG. 7. In situations wherein a PBX service Vis provided to a customer group, a flash or alert condition is .affected manually at the substation and detected by a human operator at the switchboard unit who would thereupon transfer the call. However, in automatic telephone systems of the type illustrated wherein human operators and switchboard units are not employed, it is necessary that a flash or alert condition be automatically recognized at the central oflice location.. The generation of a flash condition indication is effected through the agency of a liash device FD which is included in the subset unit of each of the substations Still through S59 and is operative to enable the transmis- 'si-on gate comprising the diode 19 for a predetermined interval of time. The ini-tial appearance of the P1 pulses at the link terminal Htl results in the generation of a HU/CPC signal as hereinabove described. The HU/ CPC signal so generated occurs at a time when the route memory of the common control unit lh indicates that al communication connection has been effected and the signal, accordingly, is resolved as a hang-up change condition indication. Referring to the time diagram of FIG. 7, the appearance of this hang-up condition appears at the central oiice at the time TG. The crosspoint connection is not, however, immediately released but rather a timing operation commences in the comm-on control unit 100' with respect to the link Lil. This timing may be etected within the common control unit le@ by any one of several means well known in the art. F or example, a physical circuit may be advantageously employed which produces a timing wave, each occurrence of which 1s effective to niark time spots in an appropriate register device contained within the common control unit lo@ which may be referred to for a determination of elapsed time.

From the above description of the generation of an HU/CPC signal, it is evident that the generation thereof resulting from the initial appearance of Pl pulses at the link terminal Htl of the switching network l results in information being stored in the route memory of the common control unit lil@ to indicate that the communication connection is to be disconnected. Accordingly, the next action to be performed in the normal sequence of the progress of a communication connection is that of releasing the crossr oint connection by the central oiT ce location. l'n this sequence, there is no further supervisory information normally expeced from the substation S59. It is evident that the ANS/CPR signal generated in respense to the release of the crosspoint connection occurs subsequent to a control operation by the entral ofce location. However, the flash device is operative after a predetermined interval of time to again inhibit the transmission gate comprising the diode i9 to prevent the appearance of the Pl pulses at the link terminal The resultant absence of the Pi pulses at the link terminal Htl results in the generation of an ANS/CPP. signal as hereinabove described. Accordingly, the tlash device may be, for example, a control switch which is capacitively timed to determine the conductive state of the transmission gate and, accordingly, the appearance of Pl pulses at the link terminal Htl. The substation S553 during this interval of time remains in an of hook state condition. The cross point connection is maintained in a closed condition until such time that an lill/CPC signal can be resolved as indicating a true hang-up change condition as distinguished 'from the initiation of a ash condition.

Referring to the time diagram or" Fi G. 7, the tolerances of the ilash device may be advantageously determined to create system conditions for the generation of an ANS/CPR signal subsequent to time Til (50 rnilliscconds) and prior to time T2 (250 milliseconds) after the generation of an HU/CPC signal. As a convenient rate of scan by each of the loop scanner 29 and link scann 35 for each of the substations through S59 anc .3 Lil through L?, respectively, is one step per two milliseconds, the link scanner 35 which is operative to detect the flash condition has a scanning cycle tin-re of 20 milliseconds. Accordingly, if the ANS/CPR signal is received prior to a predetermined time, say 5l) milliseconds after the reception of the Ell/CPC signal in order to allow for any variance in the scanning rate of the l scanner 3S, the HU/CPC signal previously received is regarded as a random disturbance and the communication connection reentered in the route rneinory of the conunon control unit as still being effected or established. However, if the ANS/CPR signal has not occurred within an arbitrary time, say 25() milliseconds, after the reception of the HU/ClC signal, the common control unit can recognize 'the Eil/CPC signal previously received as a true hangmp change indication and disconnect the communication connection or" substation S59. The ide ty of the substation SSS? which has been recorded on a link s with respect to the link Lil in the route memory of the common control unit Gd is thereupon erased and the link L@ indicated as being idle. However, if 'the ANS/CPR is received subsequent to 50 milliseconds and prior to 250 milliseconds after the reception of the HU/CiC signal, the common control unit Mill resolves this signal as indicatin a flash condition at the substation S59.

`When a flash condition has been determined as appearing on the link L@ through which the substation S539 is being provided a communication connection, the crosspoint connection is maintained closed but the link Lt) is connected at the central orhce location to a dial digit receiver, not shown, individual to the link through the central oftice switching network. rEhe previously connected substation, which may be either one of the remaining substations Sull through S538 or a substation elsewhere in the telephone system, is momentarily removed from the communication connection.

The availability of a dial digit receiver may be indicated to the substation S59 by the transmission of an identihable tone in a well-known manner thereto from the central office location. The unavailability of a dial digit receiver at the central oiiice location upon the receipt of a ilash condition from the substation S59 may be indicated by the absence of such identifiable tone. Upon a determination of the availability of a dial digit receiver, substation S59 thereupon proceeds to dial the identication of the particular substation to which the previously connected substation is to be connected, preceding this dialing operation by a predetermined dial code to indicate whether the call is to be transferred or a conference call established. Upon a dialing operation by the substation S59 having been completed and a conference call indicated, the previously connected substation is connected to a conference circuit, not shown, of a type well known in the art. A communication connection is also established by the central ohce from the conference circuit, not shown, through a crosspoint connection common to an idle link terminal H2 and loop terminal Vil to establish a communication connection along an idle link '122 to the substation Sdi). if one of the links Lil-L9 is not available for a conference call, such unavailability may be indicated by the transmission of an identifiable tone to substation S59 in a manner well known in the art. The link L@ associated with the substation S59 is similarly connected to the conference circuit, not shown, to effect the establishment of a three-way communication connection. li, however, the substation S59 does not choose to establish a conference connection, it may return to an oit-hook state condition upon the receipt of a second tone which indicates that the substation Sii@ has been identified by the central oiice location and a link is available to establish a communication connection to substation Still. The return of the substation S59 to an oit-hook state condition results in the generation of an Htl/CPC signal indica1 g a hangvvup change condition and the appropriate crosspoint connection is released in the manner hereinabove cescribed. Accordingly, the previousiy connected substation is now connected directly to he link LZ and an appropriate crossnoint connection closed in the switching network il to establish a con niunication connection therefrom to the substation Slill.

lt is to be understood that the above-described arrangement is illustrative of the application of the principles of this invention. Numerous other arrangements may be devi d by those ski..ed in the art without departing from the spirit and scope of the invention.

What is claimed is:

l. In a telephone system, a plurality of substation loops, gating means connected to each of said substation loops, each of said gating means being operative to assume a functional condition responsive to the condition of the substation loop connected thereto, a switching network, means for applying a first train ot pulses to one side of said gating means, means for applying a second train of pulses to one side of said switching network, the other side of said switching network being connected to said substation leops, and means connected to said other side of said switc .g network and the other side of said gating means for detecting the appearance thereat oi said irst train of pulses and said second train of pulses.

2. in a line concentrator telephone system, a plurality of substation loops, gating means individually connected to each of said loops so as to be in their low impedance state for one condition or said loop connected thereto and to be in their high impedance state for the other condition or said loop connected thereto, a plurality of link connectors, a switching network for connecting said link connectors and said loops, said links being connected to one side of said switching network, a. iirst source of a rst train of pulses, a second source of a second train of pulses, means for applying said first pulses to one side of each of said gating means, means for applying said second pulses to said one Side of said switching network, means including rst scanner means connected to the other side of said gating means and to the other side of said switching network for detecting the presence of said rst and said second trains of pulses, and means including second scanner means connected to said one side of said switching network for detecting the appearance on said link connectors of said lirst pulses.

3. In a line concentrator telephone system, the combination set forth in claim 2 further comprising memory means for storing information as to the state of each of said link connectors, means for scanning said memory means in synchronism with the scanning of said link connectors by said second scanner means, means for combining the outputs of said second scanner means and said memory scanning means, and means connected to said combining means for controlling the setting of said memory means.

4. in a line concentrator telephone system, the combination as set forth in claim 3 wherein said combining means includes a first and second AND gate, first and second inverting means, means for applying the output of said, second scanner means to said first AND gate and through said first inverting means to said second AND gate, and means for applying the output of said memory scanning means to said second AND gate and through said second inverting means to said first AND gate.

5. A supervisory system for a telephone system for transmitting to a central office location information respecting the change in use condition of substation loops and link connectors comprising a central ofiice location, a plurality of substation loops, a switching network having one side connected to said substation loops, a plurality of link connectors connected to the other side of said switching network and extending to said central ofiice location, means connected to said one side of said switching network for detecting a first change in use condition of said substation loops, means connected to said other side of said switching network for detecting a different change in use condition of said substation loops, and means for transmitting signals to said central ofiice indicative of said changes in use condition of said substation loops.

6. In a telephone system, a plurality of substation loops having a number of state conditions, a central oflice location having a plurality of link connectors emanating therefrom, a switching network for providing a connection between one of said loops and a preselected one of said link connectors, said networkhaving a plurality of loop terminals connected one to each of said loops and a plurality of link terminals connected one to each of said link connectors, a source of first pulsating signals, a plurality of transmission gating means corresponding one to each of said loops for connecting said source of first signals t that one of said loop terminals connected to said corresponding loop, each of said gating means being controlled by the present state condition of said corresponding loop, a source of second pulsating signals comprising delay means connecting said source of first pulsating signals to each of said link terminals, and means for scanning each of said loop terminals on a time basis for determining the appearance of said first and said second pulsating signals thereat.

7. In a supervisory system for telephone systems, a plurality of substation loops to be supervised, each of said loops having a number of state conditions, a central ofiice location having a plurality of lings emanating therefrom, a switching network having a plurality of loop terminals and a plurality of link terminals, means coupling each of said plurality of loops to a preselected one of said loop terminals, means coupling each of said plurality of links to a preselected one of said link terminals, said switching 4 network being operative to provide an interconnection between one of said loop terminals and a preselected one `of said link terminals, a first source of first pulsating signais, a second source of second pulsating signals, means controlled by the present state condition of a particular one of said loops for electrically connecting said first source to said loop terminal coupled to said particular one of said loops, means for connecting said second source to each of said link terminals, first means for determining the appearance of said first and said second signals at each of said loop terminals, second means for determining the appearance of said first signals at each of said link terminals, and means for synchronously operating said first and said second means. t

8. In a telephone system, a subscriber loop to be supervised, said loop having a first and a second state condition, a central ofiice location, switching means for establishing a communication path between said loop and said central ofiice location, signaling means adapted to be normally operative for transmitting supervisory signals to said central ofiice location, first means controlled by said loop in said first condition to inhibit said signaling means, said signaling means being therefore operative while said loop is in said second condition, and second means operative upon the establishment of said communication path and while said communication path is maintained to inhibit said signaling means.

9. In a telephone system, a substation loop having a first and a second state condition, a central office location havin-g a transmission link emanating therefrom, a switching network for interconnecting said loop and said link, said network having -a loopV terminal connected to said loop and a link terminal connected to said link, a source of first pulses, transmission gating means controlled by said loop during said first condition `for electriomly connecting said first source to said loop terminals, a source of second pulses` connected to said link terminals, means connected to said loop lterminal for determining the presence thereat of said first pulses through said transmission gating moans and said second pulses` through said network, coincident gating means responsive to pulses from said source of first pulses and from said source of second pulses for connecting said determining means to said loop terminal, and transmisison means connected to said determining means, said transmission means including inverter means whereby an indication is transmitted only upon a simultaneous absence of said first and said second pulses lat said loop terminal.

l0. -In a telephone system, a plurality of substation loops to be supervised, each of said loops having a first and a second state condition, a centr-al oiiice location having a plurality of links emanating thereform, a switching network having a plurality of loop terminals connected one to each of said loops and :a plurality of link terminals connected one to each of said links, said network being operative rto selectively connect one of said loop terminals and a preselected one yof said link tenninals by providing an internal connection therethrough, a source of first pulses, a plurality of gating means each controlled by corresponding ones of said loops in said first condition `for connecting said source of first pulses to said loop tenminal connected to said corresponding loop, a source of second pulses connected to each of said link terminals, scanner means for determining on a time basis the appearance of said first and said second pulses at each of said loop terminals, said second pulses being directed along said internal connection through said network, said scanner means including detector means for indicating the presence or absence of said first and'said second pulses, and inverter means connected to said detector means whereby an indication is only provided upon the simultaneous absence or said first and said second pulses at each of said loop terminals.k

l1. ln a telephone system in accordance with claim l() further comprising means for directing said indication to said central office location, said directing means including means for providing alternating-current pulses responsive to each of said indications and phantom circuit paths superimposed on selected pains of said links.

l2. In a 'telephone system, a plurality of substation loops to be supervised, each of said loops having a first and a second state condition, a central office location having a'lesser plurality of links emanating therefrom, a switching network having a plurality of loop terminals connected one -to each of said loops 'and a plurality of link terminalsconnected one to each of said links, said switching network lbeing operative to provide an interconnection between one of said loop terminals and a pre- 29 selected one said link terminals, means contro lcl by eaon oi said loops in said iirst condition for providing a inst series ot pulses to said loop terrnLials, rneans for provid. iv a second series of pulses to each of said link terminals, scanning rneans for determining the appearance of said iirst and said second series of pulses at each of said loop terminals on a time basis, inverter means responsive to said scanning incans for providing an indication unen the simultaneous absence of said rst said second pulses, and rne for directing said indication to said central otlice location, said directing means including gating means responsive to sfaid central or'lice location whereby said indication is directed in a time slot corresponding to said loop terminal being scanned.

I3. in a telephone system, a substation loop to be suervised having a rst and a second sta-te condition, a central oilice location, a switching networl; for connec ing said loop to .said central ofce, inliioiting ineans controlied -by said loop in said first state condition, norrnally opeative means responsive to be disabled by said inhibiting means, said norrnally operative ineens providing indication signifying a second state condition for said loop means, effective upon the operation of said network in connecting said loop to said central oice location to inhibit `said vnormally operative means, and ineens for directing said indications generated by said normally operative rncans to said central oilice location, said indications being characteristic of said loop having entered into said second state condition and a non-operation of said network.

14. ln a supervisory system, a plurality of substation loops to be sucervised, each of said loops having a first a second state condition, a central office location, a switching network having `a plurality of loop terminals tor connecting predetermined ones ot said loops to said central oiice location, means controlled by individt tl ones of said loops in said first state condition to provide a first indication at said loop terminals connected to said individual loops, rneans ellective upon said individual loop having been acted upon by said network to provide a second indication at said connected loop terminal, means selectively connectable to each of said loop terrninals on a time basis, said connectable means being responsive to said first 4and said second indications, and noropera ive signaling rneans responsive to be in l 3d by i d connectable means, said signaling means including inver r and gar ig means whereby an absence of both said 'rst and sar second indica-tions at said ronr-.ecteil loop terminal is indicated in a corresponding tinte slot to the central office.

l5. ln a telephone systern, a plurality ol substation loops, a central oice location having a jolt dity of link connectors emanating tirerefrorn, a s-W-itc g :liar/ing a plurality of loop 4terim'nals c ectcd to corresponding ones of said loops and a plu y of lini terminals connected to corresponding ones ol said link connectors, said network being operat've to connect predetermined ones of said loop tern als to preselected f s or said tir-l1 terminals, moans connected to eacli saro loop tern s for providing a detectable condition to those or" saro. loop terminals corresponding to said loops in a first state condition, said detectable condition appearing on those of said linl; terminals connected through ss'd network to said loops in `said tirst state condition, s presence of detectable c idnmn at each ol said ln r terminals on a time basis, memory means for storing information regarding the rc `rice or absence of said detectable condition at each of sai terminals, comparison means responsive to said scanner' means and to said rnelnory means for generating a 'lirst signal upon t'ne initial appearance of said detecta le condition at each of said link terminals and a second signal upon tne initial absence o` said detectable condition at eacli of said link terminals, and vmeans for directing said first and said second signals to cbronously operated with said tirs-t central odicelocation in a particular time slot corregno-rll to eacit of said link connectors.

i6. ln a telephone system in accordance with claim l5 wherein said comparison means comprises first gating means connected to said scanner means, second ga" means connected to said nternory means, first inverter rneans connecting said scanner rneans to said second gating means, and second inverter rneans connecting said niernory means to said first gating means.

i7. In a telephone system, a plurality of substation loops, a central oiiice location having a plurality of links emanating therefrom, switching means having a plurality of loop terminals connected one to each of a corresponding one of said loops and a plurality of linl: terminals connected ono to eacll or a corresponding one of said links, means connected to each of said loop terminals for providing a detectable condition thereat, said means being inhibited by eacli of said loops in a second state condition of operation so that said detectable condition appears only at those ot' said linlf` terminals connected through said network to those ol' sai-:l loop terminals in a rst state of operation, ilrst scanner means for providing an indication upon the determination of said detectable condition at each of said link terminals, memory means comprising a plurality or" memory units corresponding one to each of said link terminals for storing information regarding the state or" said detectable condition tliercat, each of said rnernory units storing a readable condition to indicate the absence of detectable condition at said corresponding link terminal, secon scanner means synscanner means for reading said information stored in said corresponding memory units, said second scanner rneans being operative to provide an indication for each readable condition, and comparison means connected to said first and said second scanner means for providing signals indicative of the appearance of an indication frorn either said iirst or said second scanner means, said comparison rneans being operative on a tirne basis.

1S. ln a telephone system in accordance with clairn 17 wherein said comparison means comprises a lirst gating means connected to said lrst scanner means and a second gating means connected to said second scanner means, first inverter ineens connecting said first scanner means to said second gating means, and second inverter means connecting said second scanner ineans to said rst gating means.

i9. ln a telephone system in accordance with claim l7 further compri ing control responsive to each operation of said comparison means for placing said corresponding niernory unit in a predetermined condition Witn respect to said corresponding link terminal.

20. ln a telephone system, a plurality of substation loops eacli having a iirst and a second state condition or" operation, a central office location having a plurality of links emanating therefrom, a switching network having a plurality of loop terminals connected one to each of said loops and a plurality of link terminals connected one to eacli of said lit1 s, said network being operative to connect a predetermined one of said loops to a preselected one of said links, cans including a Zener diode controlled by each of said loops in said first condition and a source of pulsating signals for providing a pulsating signal to loop terminal connected to said controlling loop, sai pulsating signals b ng absent from said connected loop terminal during that period in which said controlling loop is in said second condition, scanner rneans for determining the presence of said pulsating signals at each of said link ter` inals on a time basis, said scanner means including detector rneans responsive to tlie coincidence of said pulsating signals directly from said source and from said link terminals, rnernory means for providing information regarding the presence or the absence of said pulsating signals at one of said linlr terminals being presently scanned by said scanner means, comparison means responsive to said scanner means and to said memory means, said comparison means including gating means responsive to said detector means and said memory means, and means for enabling said gating means whereby the output of said comparison means is provided in a time slot corresponding to that one of said link terminals being presently scanned by said scanner means.

21. In a supervisory system, a plurality of terminal points to be supervised having a first and a second state condition, said first condition of each of said terminal points being characterized by the appearance thereat of a pulsating signal, said second condition of each of said terminal points being characterized by the absence there- -at of said pulsating signal, and means for determining a change in the state condition of each of said terminal points, said determining means comprising; detector means for sampling Athe present state condition of each of l said terminal points on a time basis, said detector means eing responsive to said pulsating signals; memory means for storing information regarding the presence or absence of said pulsating signals at each of said link terminals; and first and second gating means, said first gating means being responsive to said detector means and said memory means upon a change in state condition from the absence to the appearance of said pulsating signals at each of said terminal points, said second gating means being responsive to said detector means and said memory means upon a change in state condition from the appearance to the absence of said pulsating signals at each of said terminal points; and means for enabling said first and said second gating means on a time basis.

22. In a supervisory system for providing information to a central oflice location directly as change condition information as distinguished from state condition information, a substation" loop to be supervised, a central office location having a link emanating therefrom, a switching network having a loop terminal connected to said loop and a link terminal connected to said link to provide an interconnection therebetween, means connected to said loop terminal and controlled by said loop in a first state condition to provide a detectable condition thereat, said detectable condition being absent therefrom while said loop is in a second state condition, first means responsive to an absence of said detectable condition at said loop terminal to provide a first indication signal, means effective upon said interconnection having been established to inhibit said first means, means for determining the initial appearance or the initial absence of said detectable condition at said link terminal, said determining means including memory means for storing information as to the previous continuous presence or previous continuous absence of said detectable condition at said link terminal and detection means presently responsive to said detectable condition at said link terminal, said determining means being operative to generate a second indication signal upon the initial appearance Vand a third indication signal upon the initial absence of said detectable condition at said link terminal, transmitting means for directing said first, said second and said third indication signals to said central ofiice location, and a plurality of indicating devices located at said central ofdce location individually responsive to be operated by said first, said second and said third indication signals, respectively.

23. In a telephone system, a plurality of substation loops, each of said loops having a first and a second state condition, a switching network having a plurality of loop 'terminals connected one to each of said loops, a source vof pulsating signals, a plurality of gating means each controlled by a corresponding one of said loops in said first -state condition for effectively connecting said source to said loop terminal connected to said corresponding loop, each of said plurality of gatig means being controlled by said corresponding loop in said second state condition for efitectively disconnecting said source from said loop terminal connected to said corresponding loop, and additional means associated with each of said corresponding loops, said additional means being operative during said second state condition of said corresponding loop for further controlling said gating means controlled by said corresponding loop wliereby said source is effectively connected to said loop terminal connected to said corresponding loop for a predetermined period of time.

Z4. In a supervisory system, a substation loop, a central oiice location having a link emanating therefrom,

a switching network having a loop terminal connected to said loop and a link terminal connected to said link for providing an interconnection therebetween, first means connected to said loop terminal and controlled by said loop in a first state condition for providing a detectable condition thereat, said detectable condition being absent therefrom while said loop is in a second state condition, ashing means for further controlling said first means whereby said detectable condition is provided at said loop terminal for a predetermined time interval during said second state condition of said loop, said detectable condition appearing along an established interconnection at said link terminal, means for determining the appearance of said detectable condition at said link terminal, said determining means including memory means for storing information as to the previous continuous presence or absence of said detectable condition at said link terminal, said determining means being operative to generate a first indication signal upon the initial presence and a second indication signal upon the initial absence of said detectable condition at said link terminal, transmitting means for directing said first and said second indication signals to said central oice location.

25. In a telephone system, a central office location having a plurality of links emanating therefrom, a substation loop having first and second operational conditions, switching network means having a plurality of link terminals individually connected to said links and a loop terminal connected to said loop, said network means being operative to provide a connection between said loop terminal and a preselected one of said link terminals, means for providingcontinuous detectable conditions at said preselected link terminal responsive to the coincidence of said first operational condition of said loop and of a first operational condition of said network means, and means responsive to the detectable condition present at said predetermined link terminal for transmitting signals to said central office location indicative of a change in said detectable condition.

26. In a telephone system as in claim 25 wherein said means for transmitting signals indicative of a change in said detectable condition includes means for providing alternating-current signals, and phantom circuit paths superimposed on selected pairs of said links.

27. In a telephone system in accordance with claim 25 wherein said first condition of lsaid loop is an on-hook condition, and wherein said means for providing detectable conditions at said predetermined link terminal comprises means responsive to the on-iook condition of said loop to provide pulsating signals to said loop terminal whereby a connection of said network between said loop terminal and said predetermined link terminal operates to provide said pulsating signals to said predetermined link terminal.

28. In a telephone system in accordance with claim 18, transmitting means responsive to the output of said comparison means including bipolar transmission means for producing a first polarity signal corresponding to the operation of said first gating means and a second polarity signal corresponding to the operation of said second gating means, and a phantom circuit path superimposed on a selected pair of said links.

29. A telephone system as in claim l, wherein said gating means comprises Zener diode means connected 33 across said loop to operate in response to the operational condition thereof.

30. ln a telephone system, a plurality of substation loops to be supervised each having a iirst and a second state of operation, a central oliice having a plurality of links emanating therefrom, switching means having a plurality of loop terminals individually connected to said loops and a plurality of link terminals individually connected to said links for providing interconnections between predetermined ones of said loops and links, -means controlled by each of said loops in said first state for providing a first detectable condition at said loop terminal connected to the controlling one of said loops, means controlled by the interconnection of said network for providing said first detectable condition at an interconnected one of said link terminals and a second detectable condition at an interconnected one of said loop terminals, lirst signaling means for generating signals responsive to the detectable conditions present at said loop terminals, second signaling means operative for generating signals indicative of a change in detectable condition at said link terminals, means for synchronizing said rst and second signal generating means, and means for transmitting information indicative of said signals to said central oflice.

3l. A telephone system as in claim 30 wherein said means for providing said first and second detectable conditions comprises a source of first pulsating signals, means responsive to said iirst state at one of said loops for transferring said pulsating signals to said loop terminals connected to that one of said loops, and means for providing second pulsating signals to said link terminals; wherein said first signaling means comprises means for sequentially scanning said loop terminals for said first and second detectable conditions, gating and inverter means for producing an output responsive to the absence of both of said conditions at said loop terminals, and first transmitting means for generating signals for transfer to said central ofiice; wherein said second signaling means comprises means for sequentially scanning said link terminals for said iirst detectable condition, means for remembering the condition detected at each of said link terminals, means for comparing the present and remembered conditions at each of said link terminals, and means including bipolar transmitting means responsive to a difference in present and remembered conditions from said comparing means for generating signals for transfer to said central oiiice; and further comprising means for time synchronizing said first and second signaling means With said central ofce.

Refierenees Cited in the le of this patent UNlTED STATES PATENTS 2,688,662 Den Hertog et al. Sept. 7, 1954 2,727,094 Flowers et al. Dec. 13, 1955 2,894,072 Abbott et al. July 7, 1959 2,924,666 Brooks et al. Feb. 9, 1960 2,957,949 James et al. Oct. 25, 1960 2,962,555 Abbott et al Nov. 29, 1960 2,976,367 Bruce et al Mar. 2l, 1961 

30. IN A TELEPHONE SYSTEM, A PLURALITY OF SUBSTATION LOOPS TO BE SUPERVISED EACH HAVING A FIRST AND A SECOND STATE OF OPERATION, A CENTRAL OFFICE HAVING A PLURALITY OF LINKS EMANATING THEREFROM, SWITCHING MEANS HAVING A PLURALITY OF LOOP TERMINALS INDIVIDUALLY CONNECTED TO SAID LOOPS AND A PLURALITY OF LINK TERMINALS INDIVIDUALLY CONNECTED TO SAID LINKS FOR PROVIDING INTERCONNECTIONS BETWEEN PREDETERMINED ONES OF SAID LOOPS AND LINKS, MEANS CONTROLLED BY EACH OF SAID LOOPS IN SAID FIRST STATE FOR PROVIDING A FIRST DETECTABLE CONDITION AT SAID LOOP TERMINAL CONNECTED TO THE CONTROLLING ONE OF SAID LOOPS, MEANS CONTROLLED BY THE INTERCONNECTION OF SAID NETWORK FOR PROVIDING SAID FIRST DETECTABLE CONDITION AT AN INTERCONNECTED ONE OF SAID LINK TERMINALS AND A SECOND DETECTABLE CONDITION AT AN INTERCONNECTED ONE OF SAID LOOP TERMINALS, FIRST SIGNALING MEANS FOR GENERATING SIGNALS RESPONSIVE TO THE DETECTABLE CONDITIONS PRESENT AT SAID LOOP TERMINALS, SECOND SIGNALING MEANS OPERATIVE FOR GENERATING SIGNALS INDICATIVE OF A CHANGE IN DETECTABLE CONDITION AT SAID LINK TERMINALS, MEANS FOR SYNCHRONIZING SAID FIRST AND SECOND SIGNAL GENERATING MEANS, AND MEANS FOR TRANSMITTING INFORMATION INDICATIVE OF SAID SIGNALS TO SAID CENTRAL OFFICE. 